Many people use wireless communication devices (WCDs), such as cell phones and personal digital assistants (PDAs), to communicate with cellular wireless networks. These WCDs and networks typically communicate with each other over a radio-frequency (RF) air interface according to a wireless communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are also referred to as “1×RTT (1×) networks,” which stands for “Single Carrier Radio Transmission Technology”. These networks (referred to herein as “CDMA networks”) typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data communication.
Typical CDMA networks include a plurality of base stations, each of which provide one or more wireless coverage areas, such as cells and sectors. As a general matter, sectors are used herein as examples of wireless coverage areas. When a WCD is positioned in a sector, it can communicate over the RF air interface with the base station, and, in turn, over one or more circuit-switched and/or packet-switched signaling and/or transport networks to which the base station provides access. The base station and the WCD conduct these communications over a frequency known as a carrier.
In a typical wireless network, a WCD maintains different base-station-signal sets that typically include an active set, a candidate set, a neighbor set, and a remaining set. At a given time, the active set comprises one or more “active” sectors or coverage areas that are being used to maintain a call for the WCD. The WCD receives substantially the same information from each of the coverage areas in the active set and, on a frame-by-frame basis, selects the best signal to use. The candidate set comprises sectors that are not presently assigned to a call, but are strong enough to be used for a call. The neighbor set comprises sectors having signals that could be received with sufficient strength to enable successful communication. The remaining set comprises sectors the WCD is in communication with that are not in the active, candidate or remaining sets. The WCD, one or more base stations, and/or a base station controller maintains in memory a list of the coverage areas in the WCD's base-station-signal sets.
In existing systems, a link from the base station to the WCD is called a forward link and a link from the WCD to the base station is called a reverse link. In order to facilitate a determination of which sectors should be in the WCD's active and neighbor set, all base stations emit a pilot signal to convey a pseudorandom number (PN) offset that identifies a given sector. A WCD constantly measures the strength of each pilot signal that it receives, and notifies at least one base station when pilot strength for various coverage areas falls above or below designated thresholds. The base station, may, in turn, provide the WCD with updated lists of the sectors in the various base-station-signal sets.